CSRF filter in Play doesn't allow custom token generator

[brikis98]

For the last year or so, we've been using the CSRF filter originally created by @jto. This filter allowed the user to specify a custom token generator, which is important if your deployment includes other (non-play) apps that read your token and expect it to use a specific format.

We're upgrading to Play 2.2 and it looks like the CSRFAction class does not support a pluggable generator: it is just hard-coded to use Crypto.generateSignedToken. Would there be any objections to us submitting a pull request to add tokenGenerator: => String as a constructor parameter of CSRFAction and CSRFFilter? We could set the default value to Crypto.generateSignedToken, so it would be backwards compatible, while still allowing an injection point for this custom behavior.

[jroper]

Hi @brikis98,

I'll look at restoring this functionality today.

[jroper]

Note that the reason we switched to signed tokens is to address the BREACH security vulnerability.

[brikis98]

Thanks @jroper. Can you provide a bit more info about how the signed token helps deal with BREACH?

[jroper]

The signed token randomises the token value on each request, making it impossible to character by character ascertain what it is using a BREACH style exploit. You're vulnerable if you're using SSL with HTTP level gzip encoding.

[jroper]

See http://jazzy.id.au/default/2013/08/14/a_practical_solution_to_the_breach_vulnerability.html for more details.

[brikis98]

Hm, perhaps I'm misreading the code, but it like a new token isn't generated on each request, but only if the request doesn't already have one:

} else if (getTokenFromHeader(request, tokenName, cookieName).isEmpty && createIfNotFound(request)) {

      // No token in header and we have to create one if not found, so create a new token
      val newToken = Crypto.generateSignedToken
}

[jroper]

The raw token itself is generated once per session. However, the token is resigned on each use, see:

https://github.com/playframework/playframework/blob/master/framework/src/play-filters-helpers/src/main/scala/play/filters/csrf/csrf.scala#L58

Hence the signed token is random per request, but the raw token it's generated from is static.

[brikis98]

Ah, gotcha. Thanks for the detailed explanation.

[jroper]

@brikis98 I've implemented this, feel free to review to make sure it has what you need. Note that I've also implemented a feature to disable signing for your use case:

#1737